Bacterial populations in an anthropogenically disturbed stream: Comparisonof different seasons

To determine the effects of environmental changes on stream bacterial popul ations, assemblage-and population-level measurements were compared between an anthropogenically disturbed stream and an undisturbed reference stream d uring different seasons, Physical and chemical variables monitored at two d isturbed sites from a stream affected by multiple environmental perturbatio ns confirmed discernibly different water quality from three reference sites : two from an adjacent, undisturbed watershed and one hom the headwaters of the polluted stream. Assemblage-revel variables, including: total number o f bacteria, colony forming units, and number of Bacteria from in situ hybri dization revealed only one statistically significant difference between dis turbed and undisturbed sites. Population-level changes of three bacterial s pecies, Burkholderia cepacia, Pseudomonas putida, and Acinetobacter calcoac eticus, were determined by colony hybridization with rDNA probes. Abundance of culturable A. calcoaceticus was higher at: disturbed sites in November and February; B. cepacia. and P. putida did not exhibit pollution-associate d responses. In contrast, in situ hybridization indicated that there was mo re A. calcoaceticus at the reference sites in November and April, suggestin g that culturability of the species increased at disturbed sites. To determ ine if differences among sites were attributable to changes in water qualit y among the streams, three bacterial strains isolated from the disturbed st ream were grown for 64 h in flasks in water from disturbed and reference si tes. As observed in the stream, A. calcoaceticus numbers increased in pollu ted stream water after an initial lag period of approximately 24 h. Our res ults indicate that although assemblage-level measurements of bacterial comm unities did not reflect environmental differences among sites, A. calcoacet icus; population sizes differed between disturbed and reference sites, sugg esting that anthropogenic disturbance can alter some bacterial populations and not others.